The present invention is related to piezo-electric actuator-transducers for sound reproduction systems.
More particularly, the invention is directed to sound reproduction system applications wherein the piezoelectric actuator-transducer defines a vibration means to be secured to a panel forming part of a structure and whose vibrations would normally constitute an undesired effect. Examples of these applications are disclosed and illustrated in WO 97/16048 in the name of the same Applicant (unpublished at the priority date of the present application), wherein the panel to which the piezo-electric actuator-transducer is applied consists of a vehicle body element. In these and similar applications the piezo-electric actuator-transducer comprises in a known way a thin ceramic plate having a securing face thereof to said panel and a pair of electrodes connected to the plate. In the above-mentioned prior document examples of how the piezo-electric actuator-transducer is secured to the vibrating panel are also provided, including the aid of a structural adhesive, normally a high elasticity modulus resin, layered onto the securing face of the piezo-electric actuator-transducer to the panel.
The present invention is directed to a novel and unique expedient enabling to enhance securing of the piezo-electric actuator-transducer both in connection to a safer and more reliable anchoring thereof, and as far as easier and more convenient fixing operation thereof are concerned.
According to the invention, this object is achieved primarily by virtue of the fact that the ceramic plate of the piezo-electric actuator-transducer is fitted within a substantially tray-like container made of a relatively flexible material, having a peripheral flange provided with an adhesive layer; a seat, surrounded by said peripheral flange and having a shape complementary to that of the ceramic plate, in which said ceramic plate is housed and fixed with the securing face thereof facing to the outside of the container and arranged in a lowered plane with respect to the adhesive layer of said peripheral flange; and a receptacle interposed between said peripheral flange and said seat for the ceramic plate.
The provision of the above container enables on one hand to effectively protect the piezo-electric actuator-transducer in its installed condition and on the other hand, due to its relatively flexible construction, to make securing operation of the ceramic plate (which is instead relatively rigid and fragile) easier even onto non perfectly planar, and even curved or crowned surfaces.
Moreover the receptacle provided between the peripheral flange of the container and the seat for the ceramic plate is able to further facilitate application of the piezo-electric actuator-transducer onto the related panel, since, upon adhesion of the adhesive layer of the peripheral flange of the container against the panel onto which the piezo-electric actuator-transducer is to be applied, any excess or squeezed amount of the structural adhesive layered over the securing face of the ceramic plate is allowed to pour into the receptacle, thus being received and captured thereby. Accordingly the adhesive surfaces of the peripheral flange and of the securing face of the ceramic plate are ensured to be arranged substantially at the same level, i.e. under perfect adhesive contact with the panel to which the piezo-electric actuator-transducer is secured.
The container may be conveniently closed by a covering sheet peelably adhering to the adhesive layer of said peripheral flange and to be removed prior to securing the piezo-electric actuator-transducer onto said panel.
The receptacle interposed between the peripheral flange and the seat for the ceramic plate of the container is advantageously designed as an annular channel, and according to a preferred embodiment of the invention this annular channel is communicating with said seat for the ceramic plate through passages arranged substantially at the same level of the securing face of the ceramic plate.
Depending upon the shape of the ceramic plate, the housing may be circular, quadrangular or even polygonal.
Moreover the flange of the container, which is normally made of moulded thermoplastic material, may be formed with a passage for outer wires connected to the electrodes of the piezo-electric actuator-transducer.
The invention will now be disclosed in detail with reference to the accompanying drawings, purely provided by way of non limiting example, in which:
Referring initially to figures 1 and 2, reference numeral 1 generally designates a piezo-electric actuator-transducer according to the invention, to be employed with a sound reproduction system comprising a sound pick-up or sound receiver apparatus, an amplifier apparatus and at least one vibrating-element sound emitter, formed by a panel or the like to which the piezo-electric actuator-transducer 1 is secured in the way which will be clarified herebelow.
The vibrating panel to which the piezo-electric actuator-transducer is to be secured, diagrammatically depicted as P in figure 3, may be constituted by a structural member of motor-vehicle body or by the shall of a helmet, or by the body of an illuminating apparatus or by any other element adapted to vibrate so has to produce sounds.
The piezo-electric actuator-transducer 1 is formed, according to the invention, by a thin ceramic plate 2 of a conventional type, provided also in a way known per se with a pair of electrodes (not shown) connected to outer wires 3, and by a container 4 within which the ceramic plate 2 is fitted and permanently fixed.
In the case of the shown example the ceramic plate 2 and the container 4 have a circular design: it is however to be pointed out that the shape of either one or both may be different, for instance quadrangular or polygonal.
The ceramic plate 2 may be for instance of the type produced and marketed by Hoechst AG under the trade name Sonox® P 51 and the like.
The container 4 has a generally cup or tray-like configuration and is made of a relatively flexible material, for instance a moulded thermoplastic material. The container 4 is formed with a peripheral annular flange 5 whose face intended to be placed into contact with the panel P is covered by an adhesive layer 6 which can be constituted, for instance, by a bi-adhesive annular film.
Innerly of the peripheral flange 5, the container 4 is formed with a lowered seat 7 having a shape complementary of that of the ceramic plate 2, within which this ceramic plate 2 is housed and fixed, in correspondence of its inner face, by means of an adhesive layer 8.
As better shown in figure 3, the depth of the seat 7 is greater than the thickness of the ceramic plate 2 added to the thickness of the inner adhesive layer 8, whereby the outer face of this ceramic plate 2, designated as 2a, is arranged in a lowered plane with respect to the outer surface of the adhesive layer 6 of the peripheral flange 5. The difference in height therebetween may be normally comprised between 0.05 and 0.03 mm, and is preferably about 0.1 mm.
Between the seat 7 and the annular flange 5, the container 4 is formed with a receptacle designed as an annular channel 9, which is also lowered with respect to the peripheral flange 5. This intermediate annular channel 9 is in communication with the seat 7 through passages arranged substantially at the same level as the outer face 2a of the ceramic plate 2. In the case of the shown example, these passages are formed by a number of radial grooves 10 provided on top of the wall delimiting the seat 7.
In correspondence of the seat 7, the container 4 may be formed with outer stiffening ribs 11. Moreover the back of the annular flange 5 is conveniently provided with an integral tunnel 12 passed through by the outer wires 3.
In the condition preceding its application, depicted in figures 1 and 2, the piezo-electric actuator-transducer 1 is provided with a cover sheet 13 adhering in a peelable way to the adhesive layer 6 of the peripheral flange 5, so as to overlay the outer face 2a of the ceramic plate 2.
Upon application of the piezo-electric actuator-transducer 1 onto the panel 2, the cover sheet 13 is removed (such as shown in figure 2), so as to expose the adhesive layer 6 and the outer face 2a of the ceramic plate 2.
Then a layer of structural adhesive 14, normally comprising a high elasticity modulus resin (for instance an epoxy resin) is deposited onto the outer face 2a, such as shown in figure 4.
Thereafter the piezo-electric actuator-transducer 1 is brought into contact against the panel P, adhering thereonto the adhesive layer 6 of the peripheral flange 5, as well as the structural adhesive layer 14 applied on the outer face 2a of the ceramic plate 2. At this stage, any excess or squeezed amount of the structural adhesive 14 pours through the passages 10 into the receptacle 9, thus being captured therein. This ensures the thickness of the structural adhesive 14 to be that necessary and sufficient to fill the gap between the outer face 2a of the ceramic plate 2 and the outer surface of the adhesive layer 6 of the peripheral flange 5. Accordingly, in the fixed condition shown in figure 3, both the adhesive surfaces defined by the adhesive layer 6 and by the structural adhesive 14 are perfectly contacting the surface of the panel P.
The flexibility of the container 4, namely of its flange 5, enables accommodation, and thus a most efficient anchoring, of the piezo-electric actuator-transducer 1 even to panels P having a non perfectly planar configuration, i.e. with a curved and even crowned design.
It will be apparent from the above that the container 4 enables both to make application of the piezo-electric actuator-transducer 1 easier, and to achieve a particularly safe and reliable anchoring thereof in the applied condition. Additionally the container 4 provides efficient protection of the ceramic plate 2 in the fixed condition of the piezo-electric actuator-transducer 1 to the panel P.
Naturally the details of construction and the embodiments may be widely varied with respect to what has been disclosed and illustrated, without thereby departing from the scope of the present invention such as defined in the appended claims.